This invention relates to a magnetic disk apparatus which is used as a storage apparatus for a computer, a video apparatus or a like apparatus, and more particularly to a magnetic disk apparatus which allows high speed recording and reproduction of data.
Various magnetic apparatus are known, and an exemplary one of related art magnetic disk apparatus is described with reference to FIG. 10 which shows a general construction of a magnetic disk apparatus and FIG. 11 which illustrates tracking control of the magnetic disk apparatus of FIG. 10.
Referring first to FIG. 10, the magnetic disk apparatus 110 shown includes a plurality of magnetic disks 80 secured to a spindle 81 in a predetermined spaced relationship from each other, and a plurality of magnetic heads 82 for recording and reproduction individually provided for the magnetic disks 80. The magnetic disk apparatus 110 further includes a carriage 84 on which a plurality of pivotal arms 83 are held in a connected condition to each other, a bearing 85 for supporting the carriage 84 for pivotal motion thereon, a voice coil motor (VCM) 86 for generating a pivoting force for the carriage 84, a load beam 87 provided on each of the pivotal arms 83 which are pivoted by the voice coil motor 86, and a slider 88 provided at a free end of the load beam 87. The slider 88 is made of a ceramics material or the like, and a magnetic head 82 for recording and reproduction formed by a thin film technique or a like technique is placed at a free end of the slider 88.
Referring now to FIG. 11, each of the magnetic disks 80 employed in the magnetic disk apparatus 110 having the construction described above is circumferentially divided into sectoral data areas 91 and servo areas 92. Further, each of the servo areas 92 is divided into servo mark areas 93 and address code areas 94, in which servo marks A and B and address codes are recorded, respectively. A tracking error signal for the magnetic heads 82 is produced based on reproduction signals of several tens of the servo marks A and B located on each one circumference of each of the magnetic disks 80.
In each of the servo mark areas 93, a servo mark A and a servo mark B are provided on the opposite sides of a track center 96 of each of tracks 95. Each of the servo marks A and B is formed from a burst of repetitive magnetization reversals, and a tracking error signal for the magnetic heads 82 is obtained depending upon a difference between the recorded positions of the servo marks A and B and a magnitude of a reproduction output.
Subsequently, production of a tracking error signal mentioned above is described.
First, it is assumed that a magnetic head 82 is positioned at an odd-numbered track and is thereafter displaced to the outer circumferential side of the disk. In this instance, the reproduction signal from the servo mark A increases in magnitude while the reproduction signal from the servo mark B decreases in magnitude. However, if the magnetic head 82 is displaced conversely to the inner circumferential side, then the reproduction signal from the service mark B increases while the reproduction signal from the service mark A decreases.
Now, it is assumed that the magnetic head 82 is positioned at an even-numbered track and is thereafter displaced to the outer circumferential side. In this instance, the reproduction signal from the servo mark B increases in magnitude while the reproduction signal of the servo mark A decreases in magnitude. However, if the magnetic head 82 is displaced conversely to the inner circumferential side, then the reproduction signal from the service mark A increases while the reproduction signal from the service mark B decreases.
Consequently, the direction in which the magnetic head 82 is displaced can be discriminated from the magnitudes of the reproduction signals of the servo marks A and B and distinction between an even number and an odd number of the track address recorded in the address code area 94 of the track 95 at which the magnetic head 82 is positioned, and tracking control of the magnetic head 82 is performed based on the information.
A tracking error signal is obtained from the track address from which reproduction by the magnetic head 82 is performed and the magnitudes of the reproduction signals of the servo marks A and B as described above, and the voice coil motor 86 is driven based on the tracking error signal so that the magnetic head 82 may be positioned on the track center 96 to effect tracking control.
However, since the tracking control described above is performed for one magnetic head selected from the plurality of magnetic heads, usually the other magnetic heads are not registered fully with opposing tracks of corresponding magnetic disks. In other words, from dispersions of the mounted positions of the magnetic heads, the thermal expansions and the vibration modes of the pivotal arms and the load beams on which the magnetic heads are carried and so forth, only the selected magnetic head is controlled to a tracking condition optimum to recording and reproduction. Accordingly, simultaneous recording and/or reproduction by a plurality of magnetic heads is practically unavailable.
In recent years, as development of multimedia proceeds, demands for various video services of a high quality are increasing, and demands also for video servers or non-linear video editing systems which have higher performances and higher functions than video tape recorders are increasing for production and sending out of video information. Here, a "non-linear" system signifies a system wherein a tape is not used as a recording medium.
A disk apparatus which is superior in high speed accessing is suitable for use with a non-linear video editing system. However, even though a magnetic disk apparatus which has exhibited development as, for example, an external storage apparatus for a computer includes a plurality of built-in magnetic disks as described above, the magnetic disk apparatus allows a recording or reproducing operation only by a selected one magnetic head so that the data transferring rate is limited to approximately 30 Mbit/sec. Therefore, in order to obtain a data transfer rate of 100 Mbit/sec or more which is demanded for a non-linear video editing system or the like, a plurality of magnetic disk apparatus must operate in parallel to each other. This increases the scale and the cost of the system, and consequently, systems of the type mentioned are actually used in only limited applications.